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  <h1><a href="http://freetype.org/index.html">FreeType</a>
    Tutorial&nbsp;/&nbsp;II</h1>
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          <h2>II. Managing Glyphs</h2>


          <h3 id="section-1">1. Glyph Metrics</h3>

          <p>Glyph metrics are, as the name suggests, certain
            distances associated with each glyph that describe how to
            position this glyph while creating a text layout.</p>

          <p>There are usually two sets of metrics for a single glyph:
            Those used to represent glyphs in horizontal text layouts
            (Latin, Cyrillic, Arabic, Hebrew, etc.), and those used to
            represent glyphs in vertical text layouts (Chinese,
            Japanese, Korean, Mongolian, etc.).</p>

          <p>Note that only a few font formats provide vertical
            metrics.  You can test whether a given face object
            contains them by using the
            macro <a href="../reference/ft2-base_interface.html#FT_HAS_VERTICAL"><tt>FT_HAS_VERTICAL</tt></a>,
            which returns true if appropriate.</p>

          <p>Individual glyph metrics can be accessed by first loading
            the glyph in a face's glyph slot, then accessing them
            through the <tt>face-&gt;glyph-&gt;metrics</tt> structure,
            whose type
            is <a href="../reference/ft2-base_interface.html#FT_Glyph_Metrics"><tt>FT_Glyph_Metrics</tt></a>.
            We will discuss this in more detail below; for now, we
            only note that it contains the following fields.</p>

          <dl>
            <dt>width</dt>
            <dd>This is the width of the glyph image's bounding box.
              It is independent of the layout direction.</dd>

            <dt>height</dt>
            <dd>This is the height of the glyph image's bounding box.
              It is independent of the layout direction.  Be careful
              not to confuse it with the &lsquo;height&rsquo; field in
              the <a href="../reference/ft2-base_interface.html#FT_Size_Metrics">
                <tt>FT_Size_Metrics</tt></a> structure.</dd>

            <dt>horiBearingX</dt>
            <dd>For <em>horizontal text layouts</em>, this is the
              horizontal distance from the current cursor position to
              the leftmost border of the glyph image's bounding
              box.</dd>

            <dt>horiBearingY</dt>
            <dd>For <em>horizontal text layouts</em>, this is the
              vertical distance from the current cursor position (on
              the baseline) to the topmost border of the glyph image's
              bounding box.</dd>

            <dt>horiAdvance</dt>
            <dd>For <em>horizontal text layouts</em>, this is the
              horizontal distance to increment the pen position when
              the glyph is drawn as part of a string of text.</dd>

            <dt>vertBearingX</dt>
            <dd>For <em>vertical text layouts</em>, this is the
              horizontal distance from the current cursor position to
              the leftmost border of the glyph image's bounding
              box.</dd>

            <dt>vertBearingY</dt>
            <dd>For <em>vertical text layouts</em>, this is the
              vertical distance from the current cursor position (on
              the baseline) to the topmost border of the glyph image's
              bounding box.</dd>

            <dt>vertAdvance</dt>
            <dd>For <em>vertical text layouts</em>, this is the
              vertical distance used to increment the pen position
              when the glyph is drawn as part of a string of
              text.</dd>
          </dl>

          <p class="warning">As not all fonts do contain vertical
            metrics, the values of <tt>vertBearingX</tt>,
            <tt>vertBearingY</tt> and <tt>vertAdvance</tt> should not
            be considered reliable if <tt>FT_HAS_VERTICAL</tt> returns
            false.</p>

          <p>The following graphics illustrate the metrics more
            clearly.  In case a distance is directed, it is marked
            with a single arrow, indicating a positive value.  The
            first image displays horizontal metrics, where the
            baseline is the horizontal axis.</p>

          <div class="figure">
            <img src="metrics.png"
                 alt="horizontal layout"
                 width=388
                 height=253>
          </div>

          <p>For vertical text layouts, the baseline is vertical,
            identical to the vertical axis.  Contrary to all other
            arrows, <tt>bearingX</tt> shows a negative value in this
            image.</p>

          <div class="figure">
            <img src="metrics2.png"
                 alt="vertical layout"
                 width=294
                 height=278>
          </div>

          <p>The metrics found in <tt>face-&gt;glyph-&gt;metrics</tt>
            are normally expressed in 26.6 pixel format (i.e., 1/64th
            of pixels), unless you use the <tt>FT_LOAD_NO_SCALE</tt>
            flag when calling <tt>FT_Load_Glyph</tt>
            or <tt>FT_Load_Char</tt>.  In this case, the metrics are
            expressed in original font units.</p>

          <p>The glyph slot object has also a few other interesting
            fields that eases a developer's work.  You can access them
            through <tt>face-&gt;glyph-&gt;xxx</tt>,
            where <tt>xxx</tt> is one of the following fields.</p>

          <dl>
            <dt>advance</dt>
            <dd>This field is a <tt>FT_Vector</tt> that holds the
              transformed advance for the glyph.  That is useful when
              you are using a transformation
              through <tt>FT_Set_Transform</tt>, as shown in the
              <a href="step1.html#transformed-text">rotated text
              example</a> of part&nbsp;I.  Other than that, its value
              is by default (metrics.horiAdvance,0), unless you
              specify <tt>FT_LOAD_VERTICAL</tt> when loading the glyph
              image; it is then (0,metrics.vertAdvance).</dd>

            <dt>linearHoriAdvance</dt>
            <dd>This field contains the linearly scaled value of the
              glyph's horizontal advance width.  Indeed, the value of
              <tt>metrics.horiAdvance</tt> that is returned in the
              glyph slot is normally rounded to integer pixel
              coordinates (i.e., being a multiple of&nbsp;64) by the
              font driver that actually loads the glyph
              image.  <tt>linearHoriAdvance</tt> is a 16.16
              fixed-point number that gives the value of the original
              glyph advance width in 1/65536th of pixels.  It can be
              use to perform pseudo device-independent text
              layouts.</dd>

            <dt>linearVertAdvance</dt>
            <dd>This is the similar to <tt>linearHoriAdvance</tt> but
              for the glyph's vertical advance height.  Its value is
              only reliable if the font face contains vertical
              metrics.</dd>
          </dl>


          <h3 id="section-2">2. Managing Glyph Images</h3>

          <p>The glyph image that is loaded in a glyph slot can be
            converted into a bitmap, either by
            using <tt>FT_LOAD_RENDER</tt> when loading it, or by
            calling <a href="../reference/ft2-base_interface.html#FT_Render_Glyph"><tt>FT_Render_Glyph</tt></a>.
            Each time you load a new glyph image, the previous one is
            erased from the glyph slot.</p>

          <p>There are situations, however, where you may need to
            extract this image from the glyph slot in order to cache
            it within your application, and even perform additional
            transformations and measures on it before converting it to
            a bitmap.</p>

          <p>The FreeType&nbsp;2 API has a specific extension that is
            capable of dealing with glyph images in a flexible and
            generic way.  To use it, you first need to include
            the <a href="../reference/ft2-header_file_macros.html#FT_GLYPH_H"><tt>FT_GLYPH_H</tt></a>
            header file.</p>

          <pre>
#include FT_GLYPH_H</pre>

          <h4>a.Extracting the Glyph Image</h4>

          <p>You can extract a single glyph image very easily.  Here
            some code that shows how to do it.</p>

          <pre>
FT_Glyph  glyph; <span class="comment">/* a handle to the glyph image */</span>


...
error = FT_Load_Glyph( face, glyph_index, FT_LOAD_NORMAL );
if ( error ) { ... }

error = FT_Get_Glyph( face-&gt;glyph, &amp;glyph );
if ( error ) { ... }</pre>

          <p>The following steps are performed.</p>

          <ul>
            <li>Create a variable named <tt>glyph</tt>, of
              type <a href="../reference/ft2-glyph_management.html#FT_Glyph"><tt>FT_Glyph</tt></a>.
              This is a handle (pointer) to an individual glyph
              image.</li>

            <li>Load the glyph image in the normal way into the face's
              glyph slot.  We don't use <tt>FT_LOAD_RENDER</tt>
              because we want to grab a scalable glyph image that we
              can transform later on.</li>

            <li>Copy the glyph image from the slot into a
              new <tt>FT_Glyph</tt> object by
              calling <a href="../reference/ft2-glyph_management.html#FT_Get_Glyph"><tt>FT_Get_Glyph</tt></a>.
              This function returns an error code and
              sets <tt>glyph</tt>.</li>
          </ul>

          <p>It is important to note that the extracted glyph is in
            the same format as the original one that is still in the
            slot.  For example, if we are loading a glyph from a
            TrueType font file, the glyph image is really a scalable
            vector outline.  You can access the
            field <tt>glyph-&gt;format</tt> if you want to know
            exactly how the glyph is modeled and stored.</p>

          <p>A new glyph object can be destroyed with a call
            to <a href="../reference/ft2-glyph_management.html#FT_Done_Glyph"><tt>FT_Done_Glyph</tt></a>.</p>

          <p>The glyph object contains exactly one glyph image and a
            2D vector representing the glyph's advance in 16.16
            fixed-point coordinates.  The latter can be accessed
            directly as <tt>glyph-&gt;advance</tt></p>

          <p class="warning">Note that unlike other FreeType objects,
            the library doesn't keep a list of all allocated glyph
            objects.  This means you have to destroy them yourself
            instead of relying on <tt>FT_Done_FreeType</tt> doing all
            the clean-up.</p>

          <h4>b. Transforming &amp; Copying the Glyph Image</h4>

          <p>If the glyph image is scalable (i.e.,
            if <tt>glyph-&gt;format</tt> is not equal
            to <tt>FT_GLYPH_FORMAT_BITMAP</tt>), it is possible to
            transform the image anytime by a call
            to <a href="../reference/ft2-glyph_management.html#FT_Glyph_Transform"><tt>FT_Glyph_Transform</tt></a>.</p>

          <p>You can also copy a single glyph image
            with <a href="../reference/ft2-glyph_management.html#FT_Glyph_Copy"><tt>FT_Glyph_Copy</tt></a>.</p>

          <pre>
FT_Glyph   glyph, glyph2;
FT_Matrix  matrix;
FT_Vector  delta;


... load glyph image in `glyph' ...

<span class="comment">/* copy glyph to glyph2 */</span>

error = FT_Glyph_Copy( glyph, &amp;glyph2 );
if ( error ) { ... could not copy (out of memory) ... }

<span class="comment">/* translate `glyph' */</span>

delta.x = -100 * 64; <span class="comment">/* coordinates are in 26.6 pixel format */</span>
delta.y =   50 * 64;

FT_Glyph_Transform( glyph, 0, &amp;delta );

<span class="comment">/* transform glyph2 (horizontal shear) */</span>

matrix.xx = 0x10000L;
matrix.xy = 0.12 * 0x10000L;
matrix.yx = 0;
matrix.yy = 0x10000L;

FT_Glyph_Transform( glyph2, &amp;matrix, 0 );</pre>

          <p>Note that the 2&times;2 transformation matrix is always
            applied to the 16.16 advance vector in the glyph; you thus
            don't need to recompute it.</p>

          <h4>c. Measuring the Glyph Image</h4>

          <p>You can also retrieve the control (bounding) box of any
            glyph image (scalable or not) through
            the <a href="../reference/ft2-glyph_management.html#FT_Glyph_Get_CBox"><tt>FT_Glyph_Get_CBox</tt></a>
            function.</p>

          <pre>
FT_BBox  bbox;


...
FT_Glyph_Get_CBox( glyph, <em>bbox_mode</em>, &amp;bbox );</pre>

          <p>Coordinates are relative to the glyph origin (0,0), using
            the y&nbsp;upwards convention.  This function takes a
            special argument, the <em>bbox mode</em>, to indicate how
            box coordinates are expressed.</p>

          <p>If the glyph has been loaded
            with <tt>FT_LOAD_NO_SCALE</tt>, <tt>bbox_mode</tt> must be
            set to <tt>FT_GLYPH_BBOX_UNSCALED</tt> to get unscaled
            font units in 26.6 pixel format.  The
            value <tt>FT_GLYPH_BBOX_SUBPIXELS</tt> is another name for
            this constant.</p>

          <p>Note that the box's maximum coordinates are exclusive,
            which means that you can always compute the width and
            height of the glyph image (regardless of using integer or
            26.6 coordinates) with a simple subtraction.</p>

          <pre class="example">
width  = bbox.xMax - bbox.xMin;
height = bbox.yMax - bbox.yMin;</pre>

          <p>Note also that for 26.6 coordinates, if
            <tt>FT_GLYPH_BBOX_GRIDFIT</tt> is used as the bbox mode,
            the coordinates are also grid-fitted, which corresponds to
            the following four lines.</p>

          <pre class="example">
bbox.xMin = FLOOR( bbox.xMin )
bbox.yMin = FLOOR( bbox.yMin )
bbox.xMax = CEILING( bbox.xMax )
bbox.yMax = CEILING( bbox.yMax )</pre>

          <p>To get the bbox in <em>integer</em> pixel coordinates,
            set <tt>bbox_mode</tt>
            to <tt>FT_GLYPH_BBOX_TRUNCATE</tt>.</p>

          <p>Finally, to get the bounding box in grid-fitted pixel
            coordinates, set <tt>bbox_mode</tt>
            to <tt>FT_GLYPH_BBOX_PIXELS</tt>.</p>

          <p>[Computing <em>exact</em> bounding boxes can be done with
            function <a href="../reference/ft2-outline_processing.html#FT_Outline_Get_BBox"><tt>FT_Outline_Get_BBox</tt></a>,
            at the cost of slower execution.  You probably don't need
            with the possible exception of rotated glyphs.]</p>

          <h4>d. Converting the Glyph Image to a Bitmap</h4>

          <p>You may need to convert the glyph object to a bitmap once
            you have conveniently cached or transformed it.  This can
            be done easily with
            the <a href="../reference/ft2-glyph_management.html"><tt>FT_Glyph_To_Bitmap</tt></a>
            function, which handles any glyph object.</p>

          <pre>
FT_Vector  origin;


origin.x = 32; <span class="comment">/* 1/2 pixel in 26.6 format */</span>
origin.y = 0;

error = FT_Glyph_To_Bitmap(
          &amp;glyph,
          <em>render_mode</em>,
          &amp;origin,
          1 );          <span class="comment">/* destroy original image == true */</span></pre>

          <p>Some notes.</p>

          <ul>
            <li>The first parameter is the address of the source
              glyph's handle.  When the function is called, it reads
              it to access the source glyph object.  After the call,
              the handle points to a <em>new</em> glyph object that
              contains the rendered bitmap.</li>

            <li>The second parameter is a standard render mode to
              specify what kind of bitmap we want.  For example, it
              can be <tt>FT_RENDER_MODE_DEFAULT</tt> for an 8-bit
              anti-aliased pixmap, or <tt>FT_RENDER_MODE_MONO</tt> for
              a 1-bit monochrome bitmap.</li>

            <li>The third parameter is a pointer to a two-dimensional
              vector to translate the source glyph image before the
              conversion.  After the call, the source image is
              translated back to its original position (and is thus
              left unchanged).  If you do not need to translate the
              source glyph before rendering, set this pointer
              to NULL.</li>

            <li>The last parameter is a boolean that indicates whether
              the source glyph object should be destroyed by the
              function.  If false, the original glyph object is never
              destroyed, even if its handle is lost (it is up to
              client applications to keep it).</li>
          </ul>

          <p>The new glyph object always contains a bitmap (if no
            error is returned), and you must <em>typecast</em> its
            handle to the <tt>FT_BitmapGlyph</tt> type in order to
            access its content.  This type is a sort of
            &lsquo;subclass&rsquo; of <tt>FT_Glyph</tt> that contains
            additional fields
            (see <a href="../reference/ft2-glyph_management.html#FT_BitmapGlyphRec"><tt>FT_BitmapGlyphRec</tt></a>).</p>

          <dl>
            <dt>left</dt>
            <dd>Just like the <tt>bitmap_left</tt> field of a glyph
              slot, this is the horizontal distance from the glyph
              origin (0,0) to the leftmost pixel of the glyph bitmap.
              It is expressed in integer pixels.</dd>

            <dt>top</dt>
            <dd>Just like the <tt>bitmap_top</tt> field of a glyph
              slot, this is the vertical distance from the glyph
              origin (0,0) to the topmost pixel of the glyph bitmap
              (more precise, to the pixel just above the bitmap).
              This distance is expressed in integer pixels, and is
              positive for upwards&nbsp;y.</dd>

            <dt>bitmap</dt>
            <dd>This is a bitmap descriptor for the glyph object, just
              like the <tt>bitmap</tt> field in a glyph slot.</dd>
          </dl>


          <h3 id="section-3">3. Global Glyph Metrics</h3>

          <p>Unlike glyph metrics, global metrics are used to describe
            distances and features of a whole font face.  They can be
            expressed either in 26.6 pixel format or in (unscaled)
            font units for scalable formats.</p>

          <h4> a. Design global metrics</h4>

          <p>For scalable formats, all global metrics are expressed in
            font units in order to be later scaled to the device
            space, according to the rules described in the last
            section of this tutorial part.  You can access them
            directly as fields of a <tt>FT_Face</tt> handle.</p>

          <p>However, you need to check that the font face's format is
            scalable before using them.  One can do it with
            macro <tt>FT_IS_SCALABLE</tt>, which returns true when
            appropriate.</p>

          <p>Here a table of the global design metrics for scalable
            faces.</p>

          <dl>
            <dt>units_per_EM</dt>
            <dd>This is the size of the EM square for the font face.
              It is used by scalable formats to scale design
              coordinates to device pixels, as described in the last
              section of this tutorial part.  Its value usually is
              2048 (for TrueType) or 1000 (for Type&nbsp;1 or CFF),
              but other values are possible, too.  It is set to&nbsp;1
              for fixed-size formats like FNT, FON, PCF, or BDF.</dd>

            <dt>bbox</dt>
            <dd>The global bounding box is defined as the smallest
              rectangle that can enclose all the glyphs in a font
              face.</dd>

            <dt>ascender</dt>
            <dd>The ascender is the vertical distance from the
              horizontal baseline to the highest
              &lsquo;character&rsquo; coordinate in a font face.
              Unfortunately, font formats don't define the ascender in
              a uniform way.  For some formats, it represents the
              ascent of all capital latin characters (without
              accents), for others it is the ascent of the highest
              accented character, and finally, other formats define it
              as being equal to <tt>bbox.yMax</tt>.</dd>

            <dt>descender</dt>
            <dd>The descender is the vertical distance from the
              horizontal baseline to the lowest
              &lsquo;character&rsquo; coordinate in a font face.
              Unfortunately, font formats don't define the descender
              in a uniform way.  For some formats, it represents the
              descent of all capital latin characters (without
              accents), for others it is the ascent of the lowest
              accented character, and finally, other formats define it
              as being equal to <tt>bbox.yMin</tt>.  This field is
              negative for values below the baseline.</dd>

            <dt>height</dt>
            <dd>This field represents a <em>default line spacing</em>
              (i.e., the baseline-to-baseline distance) when writing
              text with this font.  Note that it usually is larger
              than the sum of the ascender and descender taken as
              absolute values.  There is also no guarantee that no
              glyphs extend above or below subsequent baselines when
              using this distance &ndash; think of it as a value the
              designer of the font finds appropriate.</dd>

            <dt>max_advance_width</dt>
            <dd>This field gives the maximum horizontal cursor advance
              for all glyphs in the font.  It can be used to quickly
              compute the maximum advance width of a string of
              text.  <em>It doesn't correspond to the maximum glyph
                image width!</em></dd>

            <dt>max_advance_height</dt>
            <dd>Same as <tt>max_advance_width</tt> but for vertical
              text layout.</dd>

            <dt>underline_position</dt>
            <dd>When displaying or rendering underlined text, this
              value corresponds to the vertical position, relative to
              the baseline, of the underline bar's center.  It is
              negative if it is below the baseline.</dd>

            <dt>underline_thickness</dt>
            <dd>When displaying or rendering underlined text, this
              value corresponds to the vertical thickness of the
              underline.</dd>
          </dl>

          <p>Notice that the values of the ascender and the descender
            are not reliable (due to various discrepancies in font
            formats), unfortunately.</p>

          <h4>b. Scaled Global Metrics</h4>

          <p>Each size object also contains a scaled version of some
            of the global metrics described above, to be directly
            accessed through the <tt>face-&gt;size-&gt;metrics</tt>
            structure (of type <a href="../reference/ft2-base_interface.html#FT_Size_Metrics">
              <tt>FT_Size_Metrics</tt></a>).  <em>No rounding or
            grid-fitting is performed for those values</em>.  They are
            also completely independent of any hinting process.  In
            other words, don't rely on them to get exact metrics at
            the pixel level.  They are expressed in 26.6 pixel
            format.</p>

          <dl>
            <dt>ascender</dt>
            <dd>The scaled version of the original design
              ascender.</dd>

            <dt>descender</dt>
            <dd>The scaled version of the original design
              descender.</dd>

            <dt>height</dt>
            <dd>
              <p>The scaled version of the original design text height
                (the vertical distance from one baseline to the next).
                This is probably the only field you should really use
                in this structure.</p>

              <p>Be careful not to confuse it with the
                &lsquo;height&rsquo; field in
                the <a href="../reference/ft2-base_interface.html#FT_Glyph_Metrics"><tt>FT_Glyph_Metrics</tt></a>
                structure.</p>
            </dd>

            <dt>max_advance</dt>
            <dd>The scaled version of the original design maximum
              advance.</dd>
          </dl>

          <p>Note that the <tt>face-&gt;size-&gt;metrics</tt>
            structure contains other fields that are used to scale
            design coordinates to device space.  They are described in
            the last section.</p>

          <h4>c. Kerning</h4>

          <p>Kerning is the process of adjusting the position of two
            subsequent glyph images in a string of text in order to
            improve the general appearance of text.  For example, if a
            glyph for an uppercase &lsquo;A&rsquo; is followed by a
            glyph for an uppercase &lsquo;V&rsquo;, the space between
            the two glyphs can be slightly reduced to avoid extra
            &lsquo;diagonal whitespace&rsquo;.</p>

          <p>Note that in theory kerning can happen both in the
            horizontal and vertical direction between two glyphs;
            however, it only happens in a single direction in nearly
            all cases.</p>

          <p>Not all font formats contain kerning information, and not
            all kerning formats are supported by FreeType; in
            particular, for TrueType fonts, the API can only access
            kerning via the &lsquo;kern&rsquo;
            table.  <span class="important">OpenType kerning via the
            &lsquo;GPOS&rsquo; table is not supported!</span>  You
            need a higher-level library
            like <a href="http://www.harfbuzz.org">HarfBuzz</a>,
            <a href="http://www.pango.org">Pango</a>,
            or <a href="http://www.icu-project.org">ICU</a>, since
            GPOS kerning requires contextual string handling.</p>

          <p>Sometimes, the font file is associated with an additional
            file that contains various glyph metrics, including
            kerning, but no glyph images.  A good example is the
            Type&nbsp;1 format where glyph images are stored in files
            with extension <tt>.pfa</tt> or <tt>.pfb</tt>, while
            kerning metrics can be found in files with extension
            <tt>.afm</tt> or <tt>.pfm</tt>.</p>

          <p>FreeType&nbsp;2 allows you to deal with this, by
            providing
            the <a href="../reference/ft2-base_interface.html#FT_Attach_File"><tt>FT_Attach_File</tt></a>
            and <a href="../reference/ft2-base_interface.html#FT_Attach_Stream"><tt>FT_Attach_Stream</tt></A>
            APIs.  Both functions are used to load additional metrics
            into a face object by reading them from an additional
            format-specific file.  Here an example, opening a
            Type&nbsp;1 font.</p>

          <pre>
error = FT_New_Face( library, "/usr/share/fonts/cour.pfb",
                     0, &amp;face );
if ( error ) { ... }

error = FT_Attach_File( face, "/usr/share/fonts/cour.afm" );
if ( error )
{ ... could not read kerning and additional metrics ... }</pre>

          <p>Note that <tt>FT_Attach_Stream</tt> is similar to
            <tt>FT_Attach_File</tt> except that it doesn't take a
            C&nbsp;string to name the extra file but
            an <a href="../reference/ft2-system_interface.html#FT_StreamRec"><tt>FT_Stream</tt></a>
            handle.  Also, <em>reading a metrics file is in no way
            mandatory</em>.</p>

          <p>Finally, the file attachment APIs are very generic and
            can be used to load any kind of extra information for a
            given face.  The nature of the additional content is
            entirely font format specific.</p>

          <p>FreeType&nbsp;2 allows you to retrieve the kerning
            information between two glyphs through
            the <a href="../reference/ft2-base_interface.html#FT_Get_Kerning"><tt>FT_Get_Kerning</tt></a>
            function.</p>

          <pre>
FT_Vector  kerning;


...
error = FT_Get_Kerning( face,          <span class="comment">/* handle to face object */</span>
                        left,          <span class="comment">/* left glyph index      */</span>
                        right,         <span class="comment">/* right glyph index     */</span>
                        <em>kerning_mode</em>,  <span class="comment">/* kerning mode          */</span>
                        &amp;kerning );    <span class="comment">/* target vector         */</span></pre>

          <p>This function takes a handle to a face object, the
            indices of the left and right glyph for which the kerning
            value is desired, an integer, called the <em>kerning
            mode</em>, and a pointer to a destination vector that
            receives the corresponding distances.</p>

          <p>The kerning mode is very similar to the <em>bbox
            mode</em> described in a previous section.  It is a
            enumeration that indicates how the kerning distances are
            expressed in the target vector.</p>

          <p>The default value is <tt>FT_KERNING_DEFAULT</tt>, which
            has value&nbsp;0.  It corresponds to kerning distances
            expressed in 26.6 grid-fitted pixels (which means that the
            values are multiples of 64).  For scalable formats, this
            means that the design kerning distance is scaled, then
            rounded.</p>

          <p>The value <tt>FT_KERNING_UNFITTED</tt> corresponds to
            kerning distances expressed in 26.6 unfitted pixels (i.e.,
            that do not correspond to integer coordinates).  It is the
            design kerning distance that is scaled without
            rounding.</p>

          <p>Finally, the value <tt>FT_KERNING_UNSCALED</tt> indicates
            to return the design kerning distance, expressed in font
            units.  You can later scale it to the device space using
            the computations explained in the last section of this
            part.</p>

          <p>Note that the &lsquo;left&rsquo; and &lsquo;right&rsquo;
            positions correspond to the <em>visual order</em> of the
            glyphs in the string of text.  This is important for
            bidirectional or right-to-left text.</p>


          <h3 id="section-4">4. Simple Text Rendering: Kerning and Centering</h3>

          <p>In order to show off what we have just learned, we now
            demonstrate how to modify
            the <a href="step1.html#basic-code">example code</a> that
            was provided in part&nbsp;I to render a string of text,
            and enhance it to support kerning and delayed
            rendering.</p>

          <h4>a. Kerning Support</h4>

          <p>Adding support for kerning to our code is trivial, as
            long as we consider that we are still dealing with a
            left-to-right script like Latin.  We simply need to
            retrieve the kerning distance between two glyphs in order
            to alter the pen position appropriately.</p>

          <pre>
FT_GlyphSlot  slot = face-&gt;glyph;  <span class="comment">/* a small shortcut */</span>
FT_UInt       glyph_index;
FT_Bool       use_kerning;
FT_UInt       previous;
int           pen_x, pen_y, n;


... initialize library ...
... create face object ...
... set character size ...

pen_x = 300;
pen_y = 200;

use_kerning = FT_HAS_KERNING( face );
previous    = 0;

for ( n = 0; n &lt; num_chars; n++ )
{
  <span class="comment">/* convert character code to glyph index */</span>
  glyph_index = FT_Get_Char_Index( face, text[n] );

  <span class="comment">/* retrieve kerning distance and move pen position */</span>
  if ( use_kerning &amp;&amp; previous &amp;&amp; glyph_index )
  {
    FT_Vector  delta;


    FT_Get_Kerning( face, previous, glyph_index,
                    FT_KERNING_DEFAULT, &amp;delta );

    pen_x += delta.x &gt;&gt; 6;
  }

  <span class="comment">/* load glyph image into the slot (erase previous one) */</span>
  error = FT_Load_Glyph( face, glyph_index, FT_LOAD_RENDER );
  if ( error )
    continue;  <span class="comment">/* ignore errors */</span>

  <span class="comment">/* now draw to our target surface */</span>
  my_draw_bitmap( &amp;slot-&gt;bitmap,
                  pen_x + slot-&gt;bitmap_left,
                  pen_y - slot-&gt;bitmap_top );

  <span class="comment">/* increment pen position */</span>
  pen_x += slot->advance.x &gt;&gt; 6;

  <span class="comment">/* record current glyph index */</span>
  previous = glyph_index;
}</pre>

          <p>We are done.  Some notes.</p>

          <ul>
            <li>As kerning is determined by glyph indices, we need
              to explicitly convert our character codes into glyph
              indices, then later call <tt>FT_Load_Glyph</tt> instead
              of <tt>FT_Load_Char</tt>.</li>

            <li>We use a boolean named <tt>use_kerning</tt>, which is
              set to the result of the macro <tt>FT_HAS_KERNING</tt>.
              It is certainly faster not to
              call <tt>FT_Get_Kerning</tt> when we know that the font
              face does not contain kerning information.</li>

            <li>We move the position of the pen <em>before</em> a new
              glyph is drawn.</li>

            <li>We initialize the variable <tt>previous</tt> with the
              value&nbsp;0, which always corresponds to the
              &lsquo;missing glyph&rsquo; (also
              called <tt>.notdef</tt> in the PostScript world).  There
              is never any kerning distance associated with this
              glyph.</li>

            <li>We do not check the error code returned by
              <tt>FT_Get_Kerning</tt>.  This is because the function
              always sets the content of <tt>delta</tt> to (0,0) if
              an error occurs.</li>
          </ul>

          <h4>b. Centering</h4>

          <p>Our code begins to become interesting but it is still a
            bit too simple for normal use.  For example, the position
            of the pen is determined before we do the rendering;
            normally, you would rather determine the layout of the
            text and measure it before computing its final position
            (centering, etc.), or perform things like
            word-wrapping.</p>

          <p>Let us now decompose our text rendering function into two
            distinct but successive parts: The first one positions
            individual glyph images on the baseline, while the second
            one renders the glyphs.  As we will see, this has many
            advantages.</p>

          <p>We thus start by storing individual glyph images, as well
            as their position on the baseline.</p>

          <pre>
FT_GlyphSlot  slot = face-&gt;glyph;   <span class="comment">/* a small shortcut */</span>
FT_UInt       glyph_index;
FT_Bool       use_kerning;
FT_UInt       previous;
int           pen_x, pen_y, n;

FT_Glyph      glyphs[MAX_GLYPHS];   <span class="comment">/* glyph image    */</span>
FT_Vector     pos   [MAX_GLYPHS];   <span class="comment">/* glyph position */</span>
FT_UInt       num_glyphs;


... initialize library ...
... create face object ...
... set character size ...

pen_x = 0;   <span class="comment">/* start at (0,0) */</span>
pen_y = 0;

num_glyphs  = 0;
use_kerning = FT_HAS_KERNING( face );
previous    = 0;

for ( n = 0; n &lt; num_chars; n++ )
{
  <span class="comment">/* convert character code to glyph index */</span>
  glyph_index = FT_Get_Char_Index( face, text[n] );

  <span class="comment">/* retrieve kerning distance and move pen position */</span>
  if ( use_kerning &amp;&amp; previous &amp;&amp; glyph_index )
  {
    FT_Vector  delta;


    FT_Get_Kerning( face, previous, glyph_index,
                    FT_KERNING_DEFAULT, &amp;delta );

    pen_x += delta.x &gt;&gt; 6;
  }

  <span class="comment">/* store current pen position */</span>
  pos[num_glyphs].x = pen_x;
  pos[num_glyphs].y = pen_y;

  <span class="comment">/* load glyph image into the slot without rendering */</span>
  error = FT_Load_Glyph( face, glyph_index, FT_LOAD_DEFAULT );
  if ( error )
    continue;  <span class="comment">/* ignore errors, jump to next glyph */</span>

  <span class="comment">/* extract glyph image and store it in our table */</span>
  error = FT_Get_Glyph( face-&gt;glyph, &amp;glyphs[num_glyphs] );
  if ( error )
    continue;  <span class="comment">/* ignore errors, jump to next glyph */</span>

  <span class="comment">/* increment pen position */</span>
  pen_x += slot->advance.x &gt;&gt; 6;

  <span class="comment">/* record current glyph index */</span>
  previous = glyph_index;

  <span class="comment">/* increment number of glyphs */</span>
  num_glyphs++;
}</pre>

          <p>This is a very slight variation of our previous code; we
            extract each glyph image from the slot, then store it,
            along with the corresponding position, in our tables.</p>

          <p>Note also that <tt>pen_x</tt> contains the total advance
            for the string of text.  We can now compute the bounding
            box of the text string with a simple function.</p>

          <pre>
void  compute_string_bbox( FT_BBox  *abbox )
{
  FT_BBox  bbox;
  FT_BBox  glyph_bbox;


  <span class="comment">/* initialize string bbox to "empty" values */</span>
  bbox.xMin = bbox.yMin =  32000;
  bbox.xMax = bbox.yMax = -32000;

  <span class="comment">/* for each glyph image, compute its bounding box, */</span>
  <span class="comment">/* translate it, and grow the string bbox          */</span>
  for ( n = 0; n &lt; num_glyphs; n++ )
  {
    FT_Glyph_Get_CBox( glyphs[n], ft_glyph_bbox_pixels,
                       &amp;glyph_bbox );

    glyph_bbox.xMin += pos[n].x;
    glyph_bbox.xMax += pos[n].x;
    glyph_bbox.yMin += pos[n].y;
    glyph_bbox.yMax += pos[n].y;

    if ( glyph_bbox.xMin &lt; bbox.xMin )
      bbox.xMin = glyph_bbox.xMin;

    if ( glyph_bbox.yMin &lt; bbox.yMin )
      bbox.yMin = glyph_bbox.yMin;

    if ( glyph_bbox.xMax &gt; bbox.xMax )
      bbox.xMax = glyph_bbox.xMax;

    if ( glyph_bbox.yMax &gt; bbox.yMax )
      bbox.yMax = glyph_bbox.yMax;
  }

  <span class="comment">/* check that we really grew the string bbox */</span>
  if ( bbox.xMin &gt; bbox.xMax )
  {
    bbox.xMin = 0;
    bbox.yMin = 0;
    bbox.xMax = 0;
    bbox.yMax = 0;
  }

  <span class="comment">/* return string bbox */</span>
  *abbox = bbox;
}</pre>

          <p>The resulting bounding box dimensions are expressed in
            integer pixels and can then be used to compute the final
            pen position before rendering the string.</p>

          <p class="warning">In general, the above function
            does <em>not</em> compute an exact bounding box of a
            string!  As soon as hinting is involved, glyph
            dimensions <em>must</em> be derived from the resulting
            outlines.  For anti-aliased pixmaps,
            <tt>FT_Outline_Get_BBox</tt> then yields proper results.
            In case you need 1-bit monochrome bitmaps, it is even
            necessary to actually render the glyphs because the rules
            for the conversion from outline to bitmap can also be
            controlled by hinting instructions.</p>

          <pre>
<span class="comment">/* compute string dimensions in integer pixels */</span>
string_width  = string_bbox.xMax - string_bbox.xMin;
string_height = string_bbox.yMax - string_bbox.yMin;

<span class="comment">/* compute start pen position in 26.6 Cartesian pixels */</span>
start_x = ( ( my_target_width  - string_width  ) / 2 ) * 64;
start_y = ( ( my_target_height - string_height ) / 2 ) * 64;

for ( n = 0; n &lt; num_glyphs; n++ )
{
  FT_Glyph   image;
  FT_Vector  pen;


  image = glyphs[n];

  pen.x = start_x + pos[n].x;
  pen.y = start_y + pos[n].y;

  error = FT_Glyph_To_Bitmap( &amp;image, FT_RENDER_MODE_NORMAL,
                              &amp;pen, 0 );
  if ( !error )
  {
    FT_BitmapGlyph  bit = (FT_BitmapGlyph)image;


    my_draw_bitmap( bit-&gt;bitmap,
                    bit-&gt;left,
                    my_target_height - bit-&gt;top );

    FT_Done_Glyph( image );
  }
}</pre>

          <p>Some remarks.</p>

          <ul>
            <li>The pen position is expressed in the Cartesian space
              (i.e., y&nbsp;upwards).</li>

            <li>We call <tt>FT_Glyph_To_Bitmap</tt> with
              the <tt>destroy</tt> parameter set to&nbsp;0 (false), in
              order to avoid destroying the original glyph image.  The
              new glyph bitmap is accessed through
              <tt>image</tt> after the call and is typecast to
              <tt>FT_BitmapGlyph</tt>.</li>

            <li>We use translation when
              calling <tt>FT_Glyph_To_Bitmap</tt>.  This ensures that
              the <tt>left</tt> and <tt>top</tt> fields of the bitmap
              glyph object are already set to the correct pixel
              coordinates in the Cartesian space.</li>

            <li>Of course, we still need to convert pixel coordinates
              from Cartesian to device space before rendering, hence
              the <tt>my_target_height - bitmap->top</tt> in the call
              to <tt>my_draw_bitmap</tt>.</li>
          </ul>

          <p>The same loop can be used to render the string anywhere
            on our display surface, without the need to reload our
            glyph images each time.</p>


          <h3 id="section-5">5. Advanced Text Rendering:
            Transformation and Centering and Kerning</h3>

          <p>We are now going to modify our code in order to be able
            to easily transform the rendered string, for example, to
            rotate it.  First, some minor improvements.</p>

          <h4>a. Packing and Translating Glyphs</h4>

          <p>We start by packing the information related to a single
            glyph image into a single structure instead of parallel
            arrays.</p>

          <pre>
typedef struct  TGlyph_
{
  FT_UInt    index;  <span class="comment">/* glyph index                  */</span>
  FT_Vector  pos;    <span class="comment">/* glyph origin on the baseline */</span>
  FT_Glyph   image;  <span class="comment">/* glyph image                  */</span>

} TGlyph, *PGlyph;</pre>

          <p>We also translate each glyph image directly after it is
            loaded to its position on the baseline at load time.  As
            we will see, this has several advantages.  Here is our new
            glyph sequence loader.</p>

          <pre>
FT_GlyphSlot  slot = face-&gt;glyph;  <span class="comment">/* a small shortcut */</span>
FT_UInt       glyph_index;
FT_Bool       use_kerning;
FT_UInt       previous;
int           pen_x, pen_y, n;

TGlyph        glyphs[MAX_GLYPHS];  <span class="comment">/* glyphs table */</span>
PGlyph        glyph;               <span class="comment">/* current glyph in table */</span>
FT_UInt       num_glyphs;


... initialize library ...
... create face object ...
... set character size ...

pen_x = 0;   <span class="comment">/* start at (0,0) */</span>
pen_y = 0;

num_glyphs  = 0;
use_kerning = FT_HAS_KERNING( face );
previous    = 0;

glyph = glyphs;
for ( n = 0; n &lt; num_chars; n++ )
{
  glyph-&gt;index = FT_Get_Char_Index( face, text[n] );

  if ( use_kerning &amp;&amp; previous &amp;&amp; glyph->index )
  {
    FT_Vector  delta;


    FT_Get_Kerning( face, previous, glyph-&gt;index,
                    FT_KERNING_MODE_DEFAULT, &amp;delta );

    pen_x += delta.x &gt;&gt; 6;
  }

  <span class="comment">/* store current pen position */</span>
  glyph->pos.x = pen_x;
  glyph->pos.y = pen_y;

  error = FT_Load_Glyph( face, glyph_index, FT_LOAD_DEFAULT );
  if ( error ) continue;

  error = FT_Get_Glyph( face-&gt;glyph, &amp;glyph-&gt;image );
  if ( error ) continue;

  <span class="comment">/* translate the glyph image now */</span>
  FT_Glyph_Transform( glyph-&gt;image, 0, &amp;glyph-&gt;pos );

  pen_x   += slot->advance.x &gt;&gt; 6;
  previous = glyph->index;

  <span class="comment">/* increment number of glyphs */</span>
  glyph++;
}

<span class="comment">/* count number of glyphs loaded */</span>
num_glyphs = glyph - glyphs;</pre>

          <p>Note that translating glyphs now has several advantages.
            The first one is that we don't need to translate the glyph
            bbox when we compute the string's bounding box.</p>

          <pre>
void  compute_string_bbox( FT_BBox  *abbox )
{
  FT_BBox  bbox;


  bbox.xMin = bbox.yMin =  32000;
  bbox.xMax = bbox.yMax = -32000;

  for ( n = 0; n &lt; num_glyphs; n++ )
  {
    FT_BBox  glyph_bbox;


    FT_Glyph_Get_CBox( glyphs[n], ft_glyph_bbox_pixels,
                       &amp;glyph_bbox );

    if (glyph_bbox.xMin &lt; bbox.xMin)
      bbox.xMin = glyph_bbox.xMin;

    if (glyph_bbox.yMin &lt; bbox.yMin)
      bbox.yMin = glyph_bbox.yMin;

    if (glyph_bbox.xMax &gt; bbox.xMax)
      bbox.xMax = glyph_bbox.xMax;

    if (glyph_bbox.yMax &gt; bbox.yMax)
      bbox.yMax = glyph_bbox.yMax;
  }

  if ( bbox.xMin > bbox.xMax )
  {
    bbox.xMin = 0;
    bbox.yMin = 0;
    bbox.xMax = 0;
    bbox.yMax = 0;
  }

  *abbox = bbox;
}</pre>

          <p>With the above modifications,
            the <tt>compute_string_bbox</tt> function can now compute
            the bounding box of a transformed glyph string, which
            allows further code simplications.</p>

          <pre>
FT_BBox    bbox;
FT_Matrix  matrix;
FT_Vector  delta;


... load glyph sequence ...
... set up `matrix' and `delta' ...

<span class="comment">/* transform glyphs */</span>
for ( n = 0; n &lt; num_glyphs; n++ )
  FT_Glyph_Transform( glyphs[n].image, &amp;matrix, &amp;delta );

<span class="comment">/* compute bounding box of transformed glyphs */</span>
compute_string_bbox( &amp;bbox );</pre>

          <h4>b. Rendering a Transformed Glyph Sequence</h4>

          <p>However, directly transforming the glyphs in our sequence
            is not a good idea if we want to reuse them in order to
            draw the text string with various angles or
            transformations.  It is better to perform the affine
            transformation just before the glyph is rendered.</p>

          <pre>
FT_Vector  start;
FT_Matrix  matrix;

FT_Glyph   image;
FT_Vector  pen;
FT_BBox    bbox;


<span class="comment">/* get bbox of original glyph sequence */</span>
compute_string_bbox( &amp;string_bbox );

<span class="comment">/* compute string dimensions in integer pixels */</span>
string_width  = (string_bbox.xMax - string_bbox.xMin) / 64;
string_height = (string_bbox.yMax - string_bbox.yMin) / 64;

<span class="comment">/* set up start position in 26.6 Cartesian space */</span>
start.x = ( ( my_target_width  - string_width  ) / 2 ) * 64;
start.y = ( ( my_target_height - string_height ) / 2 ) * 64;

<span class="comment">/* set up transform (a rotation here) */</span>
matrix.xx = (FT_Fixed)( cos( angle ) * 0x10000L );
matrix.xy = (FT_Fixed)(-sin( angle ) * 0x10000L );
matrix.yx = (FT_Fixed)( sin( angle ) * 0x10000L );
matrix.yy = (FT_Fixed)( cos( angle ) * 0x10000L );

pen = start;

for ( n = 0; n &lt; num_glyphs; n++ )
{
  <span class="comment">/* create a copy of the original glyph */</span>
  error = FT_Glyph_Copy( glyphs[n].image, &amp;image );
  if ( error ) continue;

  <span class="comment">/* transform copy (this will also translate it to the */</span>
  <span class="comment">/* correct position                                   */</span>
  FT_Glyph_Transform( image, &amp;matrix, &amp;pen );

  <span class="comment">/* check bounding box; if the transformed glyph image      */</span>
  <span class="comment">/* is not in our target surface, we can avoid rendering it */</span>
  FT_Glyph_Get_CBox( image, ft_glyph_bbox_pixels, &amp;bbox );
  if ( bbox.xMax &lt;= 0 || bbox.xMin &gt;= my_target_width  ||
       bbox.yMax &lt;= 0 || bbox.yMin &gt;= my_target_height )
    continue;

  <span class="comment">/* convert glyph image to bitmap (destroy the glyph copy!) */</span>
  error = FT_Glyph_To_Bitmap(
            &amp;image,
            FT_RENDER_MODE_NORMAL,
            0,                  <span class="comment">/* no additional translation */</span>
            1 );                <span class="comment">/* destroy copy in "image"   */</span>
  if ( !error )
  {
    FT_BitmapGlyph  bit = (FT_BitmapGlyph)image;


    my_draw_bitmap( bit-&gt;bitmap,
                    bit-&gt;left,
                    my_target_height - bit-&gt;top );

    <span class="comment">/* increment pen position --                       */</span>
    <span class="comment">/* we don't have access to a slot structure,       */</span>
    <span class="comment">/* so we have to use advances from glyph structure */</span>
    <span class="comment">/* (which are in 16.16 fixed float format)         */</span>
    pen.x += image.advance.x >> 10;
    pen.y += image.advance.y >> 10;

    FT_Done_Glyph( image );
  }
}</pre>

          <p>There are a few changes compared to the original version
            of this code.</p>

          <ul>
            <li>We keep the original glyph images untouched; instead,
              we transform a copy.</li>

            <li>We perform clipping computations in order to avoid
              rendering and drawing glyphs that are not within our
              target surface.</li>

            <li>We always destroy the copy when calling
              <tt>FT_Glyph_To_Bitmap</tt> in order to get rid of the
              transformed scalable image.  Note that the image is not
              destroyed if the function returns an error code (which
              is why <tt>FT_Done_Glyph</tt> is only called within the
              compound statement).</li>

            <li>The translation of the glyph sequence to the start pen
              position is integrated into the call
              to <tt>FT_Glyph_Transform</tt> instead
              of <tt>FT_Glyph_To_Bitmap</tt>.</li>
          </ul>

          <p>It is possible to call this function several times to
            render the string with different angles, or even change
            the way <tt>start</tt> is computed in order to move it to
            different place.</p>

          <p>This code is the basis of the FreeType&nbsp;2
            demonstration program
            named <a href="http://git.savannah.gnu.org/cgit/freetype/freetype2-demos.git/tree/src/ftstring.c"><tt>ftstring.c</tt></a>.
            It could be easily extended to perform advanced text
            layout or word-wrapping in the first part, without
            changing the second one.</p>

          <p>Note, however, that a normal implementation would use a
            glyph cache in order to reduce memory needs.  For example,
            let us assume that our text string is
            &lsquo;FreeType&rsquo;.  We would store three identical
            glyph images in our table for the letter &lsquo;e&rsquo;,
            which isn't optimal (especially when you consider longer
            lines of text, or even whole pages).</p>

          <p>A FreeType demo program that shows how glyph caching can
            be implemented
            is <a href="http://git.savannah.gnu.org/cgit/freetype/freetype2-demos.git/tree/src/ftview.c"><tt>ftview.c</tt></a>.
            In general, &lsquo;ftview&rsquo; is the main program used
            by the FreeType developer team to check the validity of
            loading, parsing, and rendering fonts.</p>


          <h3 id="section-6">6. Accessing Metrics in Design Font
            Units, and Scaling Them</h3>

          <p>Scalable font formats usually store a single vectorial
            image, called an <em>outline</em>, for each glyph in a
            face.  Each outline is defined in an abstract grid called
            the <em>design space</em>, with coordinates expressed in
            <em>font units</em>.  When a glyph image is loaded, the
            font driver usually scales the outline to device space
            according to the current character pixel size found in
            an <a href="../reference/ft2-base_interface.html#FT_Size"><tt>FT_Size</tt></a>
            object.  The driver may also modify the scaled outline in
            order to significantly improve its appearance on a
            pixel-based surface (a process known as <em>hinting</em>
            or <em>grid-fitting</em>).</p>

          <p>This section describes how design coordinates are scaled
            to the device space, and how to read glyph outlines and
            metrics in font units.  This is important for a number of
            things.</p>

          <ul>
            <li>&lsquo;True&rsquo; WYSIWYG text layout.</li>
            <li>Accessing font content for conversion or analysis
              purposes.</li>
          </ul>

          <h4>a. Scaling Distances to Device Space</h4>

          <p>Design coordinates are scaled to the device space using a
            simple scaling transformation whose coefficients are
            computed with the help of the <em>character pixel
            size</em>.</p>

          <pre class="example">
  device_x = design_x * x_scale
  device_y = design_y * y_scale

  x_scale  = pixel_size_x / EM_size
  y_scale  = pixel_size_y / EM_size</pre>

          <p>Here, the value <tt>EM_size</tt> is font-specific and
            corresponds to the size of an abstract square of the
            design space (called the <em>EM</em>), which is used by
            font designers to create glyph images.  It is thus
            expressed in font units.  It is also accessible directly
            for scalable font formats
            as <tt>face-&gt;units_per_EM</tt>.  You should check that
            a font face contains scalable glyph images by using
            the <tt>FT_IS_SCALABLE</tt> macro, which returns true if
            appropriate.</p>

          <p>When you call the
            function <a href="../reference/ft2-base_interface.html#FT_Set_Pixel_Sizes"><tt>FT_Set_Pixel_Sizes</tt></a>,
            you are specifying the value of <tt>pixel_size_x</tt> and
            <tt>pixel_size_y</tt> FreeType shall use.  The library will
            immediately compute the values of <tt>x_scale</tt> and
            <tt>y_scale</tt>.</p>

          <p>When you call the
            function <a href="../reference/ft2-base_interface.html#FT_Set_Char_Size"><tt>FT_Set_Char_Size</tt></a>,
            you are specifying the character size in
            physical <em>points</em>, which is used, along with the
            device's resolutions, to compute the character pixel size
            and the corresponding scaling factors.</p>

          <p>Note that after calling any of these two functions, you
            can access the values of the character pixel size and
            scaling factors as fields of
            the <tt>face-&gt;size-&gt;metrics</tt> structure.</p>

          <dl>
            <dt>x_ppem</dt>
            <dd>The field name stands for &lsquo;x&nbsp;pixels per
              EM&rsquo;; this is the horizontal size in integer pixels
              of the EM square, which also is the <em>horizontal
              character pixel size</em>, called <tt>pixel_size_x</tt>
              in the above example.</dd>

            <dt>y_ppem</dt>
            <dd>The field name stands for &lsquo;y&nbsp;pixels per
              EM&rsquo;; this is the vertical size in integer pixels
              of the EM square, which also is the <em>vertical
              character pixel size</em>, called <tt>pixel_size_y</tt>
              in the above example.</dd>

            <dt>x_scale</dt>
            <dd>This is a 16.16 fixed-point scale to directly scale
              horizontal distances from design space to 1/64th of
              device pixels.</dd>

            <dt>y_scale</dt>
            <dd>This is a 16.16 fixed-point scale to directly scale
              vertical distances from design space to 1/64th of device
              pixels.</dd>
          </dl>

          <p>You can scale a distance expressed in font units to 26.6
            pixel format directly with the help of
            the <a href="../reference/ft2-computations.html#FT_MulFix"><tt>FT_MulFix</tt></a>
            function.</p>

          <pre>
<span class="comment">/* convert design distances to 1/64th of pixels */</span>
pixels_x = FT_MulFix( design_x, face-&gt;size-&gt;metrics.x_scale );
pixels_y = FT_MulFix( design_y, face-&gt;size-&gt;metrics.y_scale );</pre>

          <p>Alternatively, you can also scale the value directly with
            more accuracy by using doubles.</p>

          <pre>
FT_Size_Metrics*  metrics = &amp;face-&gt;size-&gt;metrics; <span class="comment">/* shortcut */</span>
double            pixels_x, pixels_y;
double            em_size, x_scale, y_scale;


<span class="comment">/* compute floating point scale factors */</span>
em_size = 1.0 * face-&gt;units_per_EM;
x_scale = metrics-&gt;x_ppem / em_size;
y_scale = metrics-&gt;y_ppem / em_size;

<span class="comment">/* convert design distances to floating point pixels */</span>
pixels_x = design_x * x_scale;
pixels_y = design_y * y_scale;</pre>

          <h4>b. Accessing Design Metrics (Glyph &amp; Global)</h4>

          <p>You can access glyph metrics in font units simply by
            specifying the <tt>FT_LOAD_NO_SCALE</tt> bit flag
            in <tt>FT_Load_Glyph</tt> or <tt>FT_Load_Char</tt>.  The
            metrics returned in <tt>face-&gt;glyph-&gt;metrics</tt>
            will all be in font units.</p>

          <p>You can access unscaled kerning data using the
            <tt>FT_KERNING_MODE_UNSCALED</tt> mode.</p>

          <p>Finally, a few global metrics are available directly in
            font units as fields of the <tt>FT_Face</tt> handle, as
            described in <a href="#section-3">section&nbsp;3</a> of
            this part.</p>


          <h3 id="conclusion">Conclusion</h3>

          <p>This is the end of the second part of the FreeType
            tutorial.  You are now able to access glyph metrics,
            manage glyph images, and render text much more
            intelligently (kerning, measuring, transforming &amp;
            caching); this is sufficient knowledge to build a pretty
            decent text service on top of FreeType.</p>

          <p>The demo programs in the &lsquo;ft2demos&rsquo; bundle
            (especially &lsquo;ftview&rsquo;) are a kind of reference
            implementation, and are a good resource to turn to for
            answers.  They also show how to use additional features,
            such as the glyph stroker and cache.</p>
        </div>

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          <p>Last update: 12-Dec-2014</p>
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